LIGHTNING RIDGE, Australia — Jenni Brammall, scraping gently at the low dirt ceiling of an opal mine 60 feet underground, uncovered the find of a lifetime: the toe bone of a dinosaur that had turned to opal.

“It was like experiencing a fold in time,” Ms. Brammall said, “like reaching back 110 million years to just after its death and the last time it saw light.”

Ms. Brammall found the toe bone in 1996, when she was a student paleontologist. That dinosaur, most likely a fleet-footed, meat-eating theropod, had lived near a stream in a forest of towering conifers.

More than 100 million years ago, before the land masses of modern continents split asunder, Lightning Ridge sat on the edge of ’s inland sea. Streams were plentiful.

Now, it is decidedly inland, 450 miles northwest of Sydney on the edge of Australia’s arid outback. No river runs through it. Over the last three years, less than three inches of rain has fallen. In summer, temperatures linger above 112 degrees.

Lightning Ridge is known for its dark opals, as well as the opalized plant and animal fossils found in and around its mines. It produced Australia’s first fossil record of a mammal, a .

About 70,000 tourists visit each year: Amateur prospectors try their luck by sifting through pebbles for the opals. Older visitors come in winter for the town’s natural hot springs and warm weather.

But the town, with a population of about 3,500, has had mining booms and busts. So about a decade ago, a small committee set out to procure a steadier source of revenue.

Ms. Brammall, 47, the manager of the , is the driving force behind the plan.

From her office, a cramped one-room museum featuring modest displays of opals, fossils, maps and a large plastic dinosaur’s head munching spiky plastic grass, she points to a model of an ambitious $22.5 million opal museum. Two-thirds of the money needed will come from government grants and a third from private donors.

“When we build it, people will come for the building alone,” she said of the concrete two-story, energy-efficient edifice, which is 42,000 square feet and was designed by the husband-and-wife team Glenn Murcutt, a winner of the Architecture Prize, and Wendy Lewin.

Their plans include a two-story hothouse of prehistoric plant life, exhibition rooms and research facilities, and a vault from which valuable Australian opals will be sold. They expect 25,000 visitors in the first year.

The current museum housed in Ms. Brammall’s office — where just 5 percent of the collection is displayed — holds delicate, minuscule and beautifully detailed opalized pine cones, a theropod dinosaur’s tooth and ancient . These fossils are luminous with opal colors.

Display cases also hold opalized freshwater crayfish gastroliths, or yabby buttons, which are found only in Lightning Ridge’s opal mines. The buttons, about the size of a thumbnail, are mineral deposits that freshwater crayfish accumulate and store in their bodies.

When yabbies molt, discarding their hard shells so they can grow, the stored minerals are excreted to help harden the newly grown shell. They glow with opal hues of blues and greens, and sometimes brilliant flashes of red and yellow.

The museum holds Australia’s largest opalized dinosaur skeleton, a portion of an ornithopod’s spine, skull, limbs and ribs, still partly encased in clay. Its strangest exhibit is a top row of teeth made of opal owned by Harold Hodges, now deceased. Mr. Hodges, an opal dealer and bookmaker who also ran the local abattoir, wore the dentures in the 1960s and ’70s.

The landscape of Lightning Ridge is like no other in Australia, said Mr. Murcutt, who is based in Sydney. “The way humans have manipulated the landscape is surreal,” he said, adding that he takes his architecture students there on field trips. “The native landscape, the colors and the machinery, it is like a palette of art.”

Opal is dug from the earth in about a dozen countries including Brazil, Ethiopia, Indonesia, Mexico, Peru and the United States. But no other place in the world produces such prized black opal and opalized fossils of the same quality and quantity as Lightning Ridge, said Michael Archer, a at the University of New South Wales and a former director of the in Sydney.

“Looking into an opal is utterly mesmerizing,” Dr. Archer said.

Scientists know so little about opal — and the conditions that allow the formation of this rare, precious form of silicon dioxide, a substance that otherwise forms common materials like sand and glass — that “geologists are still scratching their heads about it,” he said.

Black opal is found in nodules, or seams, 30 to 100 feet underground, in layers beneath sandstone and clay. Lightning Ridge opal has a natural dark background, and flashes of green, blue, yellow or red through the stone.

Finding opals in Lighting Ridge may be more luck than science. Some miners believe that they can read the landscape and that a row of gum trees, with their fat waxy leaves, or a single wild orange tree growing in a field might point to opal beneath the surface, said Dave Roussel, who has owned several mines.

“Trees will get their roots down, looking for water in a fault line,” Mr. Roussel said. As water seeps into the earth through sandstone, it collects silica. It may then pool when it hits impervious clay, and form opals. No one is sure how long it takes for opals to form.

Lightning Ridge opals have been mined since about 1901. But prices peaked only in the 1990s, when a miner could cram “$1 million into a matchbox” in one- and two-carat stones, said Len Cram, a local author.

The new museum, on an old opal field known as Three Mile, will help keep fossils in Lightning Ridge, where scientists can continue to study them. It is expected to be completed by 2020.

“Only about one in a billion living things leaves a trace after it dies,” Ms. Brammall said. “In Lightning Ridge we have plant and animal fossils, which is rare. To have opals is very rare. To have opals and fossils combined is astounding. They need a home here.”